Is there a reason that visual programming languages haven’t taken off for professional programming? I know of several for specific fields (Dark for backends, TouchDesigner for live graphics/multimedia), but none that are more generalised, open, or in wide use. It feels like an underdeveloped area that’s ripe for exploration and experimentation.
Do you know vvvv gamma? It's a visual programming environment for .Net. Its language (called VL) combines dataflow programming with features known from object-oriented and functional programming.